Question

If the total fertility rate is 1.3 and the only way people die is of old age, how big will the fourth generation (the great-grandchildren) be?

Answer 1

Lets say, the first generation has 1 million people
the second will have = 1 mil x 1.3/2.0=650,000
The third = 650,000 x 1.3/2.0= 422,500  
The fourth= 422,500 x1.3/2.0 = 274,625